Advantages of Synchronous Motors

Advantages of Synchronous Motors:

1. These motors can be made to operate at leading power factor and thereby improve the pf of an industrial plant from one that is normally lagging to one that is close to unity.

2. This motor operates at a constant speed, irrespective of load, from no-load to full load.

3. Electromagnetic power varies linearly with the applied voltage.

4. These motors can be constructed with wider air gapes than induction motors making them mechanically better.

5. Efficiency of operation is usually high, especially in the low speed and unity power factor ranges.

Disadvantages of Synchronous Motors:

1. These motors cannot be used for variable speed jobs as there is no possibility of speed adjustment

2. It requires external source for supplying dc excitation

3. It cannot be started under load, the starting torque being zero

4. It has a tendency to hunt.

5. It may fall out of synchronism and stop when over-loaded.

6. Collector rings and brushes are required.

7. For some applications these motors are not desirable as for driving shafts in small work-shops having no power available for starting and in cases where frequent starting or strong starting torque is required.